This invention relates to a continuous method of manufacturing a coil type slide fastener chain which when cut to length and provided with sliders and stops produces modern type zippers.
Coil type slide fasteners have heretofore been manufactured by initially hot forming or thermosetting synthetic plastic monofilaments to their coil or helical configuration. These heat treated coils may then be coupled together and affixed to the edges of fabric tapes, providing a continuous length slide fastener chain which is collected by loosely coiling for further processing. Invariably, dyeing of the fastener chain is accomplished by batch processing, known as package or skein dyeing. Unfortunately, these prior processes frequently result in fasteners which have a relatively high failure rate and the coils have a tendency to pop open when folded or stressed. It has been found that one of the major factors contributing to this tendency is the excessive brittleness of the monofilament coils which results from multiple exposure of the coils to excessively high processing temperatures. In this connection, the filaments are subjected to elevated temperature during the coiling state, such as when the monofilament is wound around a heated mandrel or on a mandrel disposed in heated zone. High temperature on the order of 180.degree.-200.degree. F. have been used to insure that the coil will remain in its helical configuration so that the pairs of coils can be interlocked and sewn onto the fabric tapes. Subsequently, the coil and tapes are again subjected to high temperatures during final thermofixing of the coil and again during batch dyeing, scouring and calendering. On each occasion there is apparently a partial advance of the cure of the thermosetting resin which forms the coil. It will be realized that such heat treatment causes changes in the molecular structure of the material and thus tends to make it excessively rigid or brittle and also adversely affects its receptivity to dye stuffs.
This alteration in the dye receptivity of monofilament coils manifests itself in the zipper product which has been manufactured by the processes heretofore available. After skein or batch dyeing of such zipper chain, one finds that the coil and fabric are generally not uniform in shade. Frequently the tapes are streaky or blotchy and usually have a deeper shade of color than the coil and zippers of this appearance are not commercially acceptable to discriminating consumers.
Accordingly, it is a principal object of the present invention to provide a continuous process for manufacturing coil type slide fasteners which overcomes the deficiencies of the prior art.
It is another object of this invention to provide a process for manufacturing coil type slide fasteners which produces fasteners of uniform quality both from the operational and appearance standpoints.
It is a further object of this invention to provide a process for the manufacture of slide fasteners of the above type in which the quality of the product can be continuously monitored and controlled to obtain uniform product quality.